Aiming at Fusion Power Tokamak

Aiming at Fusion Power Tokamak Design Limits of a Helium-cooled Large Area First Wall Module Clement Wong General Atomics International Workshop on MFE Roadmapping in the ITER Era Princeton University, Princeton, NJ, U.S.A., 7-10 September 2011 1

Looking from the Inside Out n+ 6 Li = 4 He + T n+ 7 Li = 4 He + T + n } Blanket 2

Low-Activation Structural Materials for Fusion R.J. Kurtz PNNL 3

Operating Range, Irradiated Structural Materials Non-negligible Neutron radiation damage SS 316 can Have significant Swelling at low neutron fluence L. Snead, ORNL 4

He Brayton Cycle for Fusion Application For comparison: Fort St. Vrain HTGR (1981-1989), He pressure @ 4.8 MPa, Tin/Tout: 405ºC/775ºC, Steam Rankine cycle DCLL He @ 8 MPa Simplified Brayton Cycle (CCGT) at He pressure of 18 MPa Gross η th versus He pressure and Tout 5

Advanced Materials and Blanket Designs SiC/SiC composite Low activation blanket design K th not high enough to take high surface heat flux Radiation damage from 14 MeV neutrons can be severe 1994 Li-W-alloy design Low pressure @0.05 MPa Neutron wall loading @ 10 MW/m 2, surface loading @ 2 MW/m 2 2-D TBR=1.37, Li Tout @ 1200 C, liquid can be converted to He @ 700-800 C Li vapor can be converted to He @ ~1000 C, resulting in th -gross ~57.7% Don t know how to fabricate with W-alloy 2002 6

Test Blanket Systems Testing in ITER Era Tritium Breeding Blankets are complex components, subjected to very severe working conditions, needed in DEMO but not present in ITER ITER is a unique opportunity to test breeder blanket mockups in DEMO-relevant conditions : Test Blanket Modules (TBMs) It is one of the ITER missions : ITER should test tritium breeding module concepts that would lead in a future reactor to tritium self-sufficiency, the extraction of high grade heat and electricity production. All the activities related to this mission form the TBM Program. All ITER Members participate in the TBM Program Definition: Each TBM and the associated ancillary systems (cooling system, tritium extraction system, measurement systems, etc..) are defined as Test Blanket System (TBS) L. Giancarli et al.,tbss/iter Interfaces, ISFNT-9, Dalian, Oct. 14, 2009 7

Test Blanket Systems Testing in ITER The 6 TBSs to be installed in ITER during H/He phase are the following: (PM : Port Master, TL : TBM Leader) Port No. and PM TBM Concept TBM Concept 16 (PM : EU) HCLL (TL : EU) HCPB (TL : EU) 18 (PM : JA) WCCB (TL : JA) DCLL (InCo : US (KO))* 2 (PM : CN) HCCB (TL : CN) LLCB (TL : IN) *InCo=Interfaces Coordinator (=TBM delivery not committed) HCLL : Helium-cooled Lithium Lead, HCPB : He-cooled Pebble Beds (Ceramic/Beryllium) WCCB : Water-cooled Ceramic Breeder (+Be), DCLL : Dual Coolant (He & LiPb) Lithium Lead HCCB : He-cooled Ceramic Breeder (+Be), LLCB : Lithium-Lead Ceramic Breeder (DC type, He & LiPb) In order to be representative of the corresponding DEMO breeding blanket, all Test Blanket Modules are required to use Ferritic/Martensitic steels è These types of steels are Ferromagnetic and therefore their presence induces a magnetic field that interferes with the main ITER magnetic field needed for confining the plasma L. Giancarli et al.,tbss/iter Interfaces, ISFNT-9, Dalian, Oct. 14, 2009 8

Solid Breeder Blankets for DEMO from ITER Parties FW surface heat flux ~0.5-0.7 MW/m 2 and large modules Ref: TBWG during ITER ITA phase, Working Subgroup 1, Assessment report on Solid Breeder Blankets, Compiled by: L.V. Boccaccini, March 2006 9

Liquid Breeder DEMO Blankets from ITER Parties FW surface heat flux ~0.5-0.7 MW/m 2 and large modules Ref: C. Wong et al., Overview of Liquid Metal TBM concepts and programs, Fus. Engr & Design 83 (2008) 850-857 10

0.5 m width for ITER TBM and m size width for DEMO/Reactor Blanket 0.484 m (W) 1.66 m (H) 0.35 m thick DCLL TBM ITER ~1.5 m (W) ~1 m (H) ~0.8 m thick DCLL DEMO module ARIES-RS 11 109-11/CW/rs 034-11/CW/jy

ITER has Helped to Focus World Fusion Resources it has Also Identified Critical Issues when Extended to DEMO?? FNSF DEMO Fusion Power Reactor 12 109-11/CW/rs 034-11/CW/jy

Distribution of ITER FW Panel Design Heat Load PFMC-13-9-13 May 2011-Rosenheim-R. Mitteau

Design Heat Load on ITER Blanket/Shield R. Mitteau @ PFMC-13 14

PSI Main Chamber Edge-localized Mode (ELM) Loads Clearly present in higher triangularity configurations ELM free H-mode and QH mode: are also being studied R.A. Pitts, 19th PSI conference May 2010, San Diego J. G. Watkins, 19th PSI conference Poster P2-66 R. A. Pitts et al., APS 2007 15 109-11/CW/rs 034-11/CW/jy

Basic Questions on the DEMO Chamber Wall Heat Flux Based on the physics and the projection of plasma edge control, what would be the corresponding projected steady state heat flux distribution for FNSF and DEMO? (The projection has to be extended from a 500 MW fusion ITER device to a ~3000 MW fusion DEMO device) What would be the temporal pulse and local heat flux distributions that the FW will have to be designed for, including startups/shutdowns and transient events? What are the heat removal design limits of a conventional large area helium-cooled FW/blanket design? 16

Simplest Input Coolant Channel Geometry for DEMO FW 4 mm 2 cm 2 cm 17

Input Chamber Wall Materials K th and Temperature Limits 1 This is a conservative value reduced from a value of ~100 W/m.K at 1000 C 2 Lower temperature limit based on radiation hardening/fracture toughness embrittlement [4] Potential materials layer, thickness TBD Interface materials undefined and assumes perfect contact 3 Upper temperature limit based on 150 MPa creep strength (1% in 1000h) [4] Ref [4] S. J. Zinkle and N.M. Ghoniem, Fus. Eng. Des. 51-52 (2000) 55. 18

He Coolant Power Input Parameters Helium: Pressure @ 8 MPa He Tin@ 350 C He velocity @ 100 m/s He thermal/physical properties as a function of local Temperature Power input: Heat flux Volumetric power from a n of 3 MW/m 2 19

He Coolant Heat Transfer Enhancement and Assumptions For 1-sided 2-D roughening Assume: h=2*h, f=1.5*f h: heat transfer coefficient f: friction factor 20

Case 1: 4 mm FS without h enhancement, L=1m, φ max ~ 0.49 MW/m 2 Case 2: 4 mm FS with h enhancement, L=1m, φ max ~ 0.62 MW/m 2 Case 1 Case 2 Tmax, C Tmax, C Heat flux, MW/m 2 Heat flux, MW/m 2 21

Case 3: 2 mm each FS, ODFS, W without h enhancement, L=1m, φ max ~ 0.63 MW/m 2 Case 4: 2 mm each FS, ODFS, W with h enhancement, L=1m, φ max ~ 0.92 MW/m 2 Tmax, C Case 3 W Case 4 ODFS RAFS Tmax, C W ODFS RAFS Heat flux, MW/m 2 Heat flux, MW/m 2 22

Case 5: 2 mm each FS, ODFS, W with h enhancement, L=0.5 m, φ max ~ 1.02 MW/m 2 Case 6: 2 mm each FS, ODFS, W with h enhancement, L=0.1 m, φ max ~ 1.1 MW/m 2 W Case 5 Case 6 W ODFS ODFS Tmax, C RAFS Tmax, C RAFS Heat flux, MW/m 2 Heat flux, MW/m 2 Plasma -> Boundary->PMI ->PFC ->Materials ->FW H/T->Blanket->Coils>Power conversion->general 23

Case 7: 3 mm ODFS + 2 mm W, Enhanced h and l=1 m Tmax, C Heat flux, MW/m 2 W ODFS With the use of ODFS as the structural material the φ max ~1.35 MW/m 2 Example: @ Location A and φ=1.25 MW/m 2 h=13690 W/m 2.K He Tin=350 C He Tout =382.6 C ΔT-film= 100.9 C ΔT-ODFS=194.2 C Tmax-ODFS=677.7 C 24

Observations from Heat Transfer Results For the conventional/typical helium cooled first wall channel design, with RAFM steel as the structural material, and with heat transfer enhancement, it is projected that the design can handle surface heat flux of ~0.62 MW/m 2 For multilayer designs with the use of RAFM steel, ODFS and W-alloy layers, the heat flux handling capability can be extended to ~0.92 MW/m 2 The reduction of flow path length could improve the heat flux removal capability to ~1.1 MW/m 2, but the increased pressure drops and pumping power and the corresponding increase in the number of blanket modules make this an unattractive approach With the successful development of ODFS as the structural material and W-alloy is used as the coating material, the heat removal capability could be extended to ~1.35 MW/m 2 25

Observations from Heat Transfer Results Based on the ITER design specific surface heat flux design of 1-5 MW/m 2 with a 500 MW-fusion machine, there is a disconnect when compared to the conventional/typical projection of ~0.5 MW/m 2 for DEMO, which could be a 3000 MW-fusion machine Limitation on surface heat removal capability is due to the minimum temperature limit of 350 C for RAFS and ODFS, and the corresponding maximum allowed temperatures limits of 550 C and 700 C, respectively The use of ODFS and W-alloy will have higher heat removal capabilities but their use as structural material will have to be demonstrated This presentation is mainly focused on the steady state operation of the FW design; the corresponding assessment on startup, shutdown and different transient effects will have to be performed 26

Key Observation The heat flux removal capability of Helium cooled chamber wall design is limited by the present sole acceptable structural material of Reduced Activation Ferritic Martinsitic (RAFM) Steel 27

Recommendations A concerted effort is needed to quantify the chamber wall heat flux distributions from present tokamaks as a function of different modes of plasma operation and changes in SOL thickness. The aim is to identify a uniform radiation design and corresponding regime of high performance. A joint core/boundary physics and FW/blanket design study should be initiated to look into design details, including: projection of optimum radiation uniformity, impacts to front face surface topology, heat removal module design and support, including impacts to tritium breeding for FNSF and DEMO. In concert with the above, a detailed review should be performed on the capability of helium-cooled first wall designs for FNSF and DEMO. Innovative high heat flux removal designs should be considered. For structural material development, ODFS structure and W coating should be emphasized in coordination with the developmental schedule of ITER-TBM, FNSF and DEMO. If the chamber wall surface heat flux is projected to be higher than 1 MW/m 2, water should be reconsidered, perhaps for even partial coverage, as the first wall and divertor coolant for the FNSF and DEMO designs* (*It should be noted that 1 mm thickness increase of metallic FW is ~0.5% reduction in TBR 1 ) 1 M. E. Sawan, Fu. Engr. & Design 81 (2006) 1131-1144 28

We Need to Provide Technical Connections Between Present and Future Tokamaks High Neutron Fluence will Limit Material Performance 29

Aiming at Fusion Power Tokamak Addressing disconnects Significant progress has been made in fusion power generation development in the last 40 years Fusion power generation is entering a very challenging period of development No doubt: a physics, material, technology, safety, testing and licensing integrated approach is necessary, taking ITER as an example In parallel with the effort on ITER, the community should continue to identify potential physics and technology disconnects, and to address them in a coordinated manner The chamber heat flux distribution and the helium-cooled heat removal capability at the chamber wall is identified as a relatively new disconnect We need to continue identifying and resolving other significant disconnects in order to pave the way to a credible fusion power development including FNSF and DEMO 30